1. Field of the Invention
The present invention relates to a high-frequency multi-selection prescaler. By using the prescaler, a divide ratio of the whole circuit can be controlled more effectively to obtain a divided frequency desired by a user.
2. Description of the Related Art
Recently, applications of high frequency technologies have grown rapidly because of the high advancement and development of electronic circuits and telecommunication systems. However, various frequency divider circuits are needed to process high frequency signals in a frequency synthesizer. Therefore, frequency dividers are broadly used in high frequency circuits. In particular, as great progress has been made in the field of electronic equipments such as computers and telecommunication devices, the configuration of frequency dividers has become a critical technique in high frequency circuit designs.
The technology of frequency divider circuits has been developed over the past decades and has been widely used in high frequency circuits. Typically, a prescaler is designed with a fixed divide ratio. FIG. 1A shows a conventional high frequency prescaler disclosed in U.S. Pat. No. 6,462,595. In the circuit of FIG. 1A, the divide ratio is fixed at 64/65, as shown in the truth table of FIG. 1B, and thus no other divide ratios are available for selection. In other words, the divide-by-64/65 prescaler does not provide any flexibility in the selection of divide ratios.
As can be seen from the above conventional circuit, current prescaler technologies fail to provide multiple divided frequencies on user demand. When a divide ratio other than the ratio of 64/65 is required by a user, the prescaler circuit has to be re-designed and the resulting re-designed divider has to be re-manufactured, which is time-consuming and also increases the cost. Therefore, in view of the above disadvantages, the inventor has proposed an inventive method and a novel apparatus to solve the problems with a simple structure at low cost, which can be utilized in a prescaler to provide a flexible divide ratio selection so that the prescaler does not need to be redesigned for each of the different divide ratios. As a result, a prescaler can be made with more flexibility and the manufacturing cost can be effectively reduced.
The present invention relates to a high-frequency multi-selection prescaler having a flexible divide ratio which can be controlled by a simple circuit for a user to easily obtain a desired frequency. By using a multi-bit selection signal with different logic levels, the divide ratio in a prescaler can be controlled on user demand.
Therefore, the high-frequency multi-selection prescaler according to the present invention is designed with a variable divide ratio for a user to obtain the desired frequency. The object of the present invention is to provide a divider circuit with expanded frequency selections, in which the divide ratio of the whole circuit can be effectively controlled through a selection switching means having a multi-bit selection signal input. To achieve the above object, the high-frequency multi-selection prescaler of the present invention comprises a first frequency divider for receiving an input signal and generating an output signal with a divided frequency through a frequency division process A second frequency divider is connected to the first frequency divider for performing a further frequency division process to the output signal from the first frequency divider on the basis of a selection switching means having a plurality of selection signals and a plurality of AND gates to form a divider circuit having expanded frequency selections. A module control performs a logic operation on the plurality of selection signals and an external control signal (MC) by an OR gate and sending an operation result to the first frequency divider to further control the divided frequency of the first frequency divider. An output selection circuit connected to the second frequency divider for performing a signal output selection in accordance with the plurality of selection signals. Thereby, the divided frequency desired by the user can be obtained and the reduction in manufacturing cost can be achieved.